This invention relates to a window or sash lock assembly and, more specifically to such an assembly which cannot be opened from the window exterior by potential burglars and the like.
The problem of securing windows and especially sash type windows from unlocking due to manipulation of the sash lock from the window exterior has been well known in the prior art and many potential solution of this problem appear in the prior art.
A first example of such a sash lock is shown in the patent of Subliskey (U.S. Pat. No. 6,116,665) which has a housing, a rotating assembly mounted in the housing, the rotating assembly including a handle rotatable in the housing and movable between open and closed position, a shaft connected to the handle and rotatable with the handle, a cam connected to the shaft, and contoured to engage a keeper, a slide plate mounted to the housing and slidable between a retracted position in which it is within the housing and an extended position in which it projects from the housing, a pin extending from one of the rotating assembly and the slide plate and a recess formed in the other of the rotating assembly and the slide plate, the pin and recess cooperating to drive the slide plate between its retracted and extended positions as the handle moves between its open and closed positions wherein the recess has a shape which causes the slide plate to be stationary during one part of the rotation of the handle as the handle moves between its open and closed positions and which causes the slide plate to move between its retracted and extended positions during another part of the rotation of the handle as the handle moves between its open and closed position. A problem with this device is that the two protruding guide rails into which the slide is snapped control the throw of the slide and can cause binding since the drive pin on the bottom of the cam that operates the slide is off center. If the slide binds, the sash lock will not securely lock the sashes or prevent the sashes from being opened. Also, since the slide is generally made of plastic material with no means of control of the vertical movement, and since the drive pin only protrudes about half way into the plastic slide, the pin may not stay in the drive hole, resulting in the slide either not projecting completely into the keeper, as intended, or not retracting from the keeper, resulting in the window remaining locked and inoperable.
A similar type of sash lock is disclosed by Rotondi (U.S. Pat. No. 6,142,541) wherein the lock is securable to a window sash of a double hung window, the lock having a base securable to that window sash. A cam is pivotable about a first axis relative to the base between an open position and a locking position, the cam pivoting in a first direction about the first axis when moving from the open position to the locking position and in the locking position including a portion extending from the base and adapted to cooperate with a keeper secured to the other window sash of the double hung window when the base is secured to the one window sash to lock the one window sash in a closed position relative to the other window sash. A guard member is pivotable about a second axis spaced from and substantially parallel to the first axis which is responsive to pivoting of the cam, the guard member being movable between a guarding position when the cam is in the locking position and a retracted position when the cam is in the open position. The guard member extends from the base to substantially overlap with the cam extending portion in the guarding position and the guard member does not substantially extend from the base in the position and the follower connection between the cam and the guard member pivoting the guard member about the second axis between the guarding position and the retracted position when the cam pivots about the first axis between the locking position and the open position, the follower connection being adapted to bias the cam toward pivoting in the first direction when a force biases the guard member toward the retracted position. As with the Subliskey patent discussed above, there is no means of controlling vertical movement of the unsupported end of the pivotal guard plate making it possible that the engagement pin on the underside of the cam can disengage from the pivotal guard plate, causing it to either not project/retract in part or in whole into/from the keeper respectively, thus preventing the window from locking or unlocking, respectively.
A patent to Mosch (U.S. Pat. No. 4,801,164) describes a check rail lock having a casing with a detent, a handle rotatable in the casing and held in a selected rotative position by a spring washer, a shaft rotatable by the handle, a cam rotatable between locked and unlocked positions the spring washer between the housing and cam and fastened to the shaft for rotation with the cam, the spring washer having an annular body with a generally concave configuration to provide a predetermined spring load on the handle, the annular body further having a pair of planar sections connected by a bend to adjacent sections thereof and detents embossed in the planar sections which coact with the detent. The spring design is complex and difficult to manufacture with consistent results due to the use of diametric detents on an opposing bi-planar surface opposite the concave face of the main spring body.